Rechargeable batteries (or storage batteries) are used in a variety of applications, such as in vehicles, tools, personal consumer devices, uninterruptible power supplies, etc. One emerging application for these batteries is in grid energy storage applications such as load leveling, where the batteries store electric energy for use during peak load periods, and in renewable energy uses, where the batteries store power generated from photovoltaic arrays during the day to be used at night.
A typical rechargeable battery includes an electrode assembly, which includes positive and negative electrode plates, a separator and an electrolyte. A problem with typical rechargeable batteries is that the reactions in these batteries are not completely reversible so that the charge-discharge efficiency of the battery reduces as the battery goes through many cycles. Furthermore, the charge-discharge efficiency of these batteries reduces markedly when the battery is below 90% State of Charge or SOC. On tests for photovoltaic application of lead acid batteries by the Sandia National Laboratories of Albuquerque, N. Mex., battery charging efficiency can be lower than 50% if charging is below the 90% SOC.
In more recent time, attempts have been made to produce liquid batteries where the energy is stored in the electrolyte and where the charge-discharge reactions are completely reversible. For example, U.S. Pat. No. 4,786,567 discloses a liquid battery in which the sulfuric acid electrolyte on the positive electrode contains vanadium ions V(5+)/V(4+) and the sulfuric acid electrolyte on the negative side contains the vanadium ions V(3+)/V(2+). The positive and negative electrodes are separated by an ionic membrane. A further development of this technology is disclosed in PCT patent application no. WO 03/019714 which discloses a redox battery where the electrolyte on the positive electrode contains a mixture of halides in hydrochloric acid while the hydrochloric acid electrolyte in the negative electrode consists of vanadium ion V(3+)/V(2+). Again, the positive and negative electrodes are separated by an ionic membrane.
Unfortunately, the use of a membrane or diaphragm in these liquid batteries creates high impedance resulting in lower energy efficiency and also lower capacity for the battery because of the slow diffusion process when a diaphragm or membrane is interposed between the positive and negative electrodes. As a result, the power capacity of the battery is reduced and a larger battery is required for a given power capacity. Furthermore, there may be some diffusion of ions through the membrane between the positive and negative electrolytes which may result in the electrolytes being contaminated.
There is a need for an electrical energy storage device or battery that overcomes or at least ameliorates at least one of the problems associated with prior art storage devices or batteries.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in any country before the priority date of each claim of this application.